This invention relates to flow control devices in which two or more liquids are moved or pumped from their individual sources of supply to a common discharge outlet. The invention is concerned more particularly with a control system for a mobile supply source for agricultural purposes such as are commonly used for supplying of fertilizers and weed and pest controls to lawns and gardens.
During approximately the past decade a large industry has developed in the treatment of lawns by companies specializing in this business. A typical lawn care program involves several treatments during the year which are typically as follows:
Early Spring--Crabgrass control, fertilization. PA0 Late Spring--Broadleaf weed control, fertilization. PA0 Summer--Weed control, insect control, fertilization. PA0 Fall--Broadleaf weed control, fertilization. PA0 (1) Variable Flow--must meter chemicals at variable flow rates while maintaining precise mixture ratios. PA0 (2) Proportion Small Flow Rates--must meter small amounts of chemicals (e.g., 0.25 to 2 ozs./gal.) in proportion to the large fertilizer flow (up to 3 to 5 gals./per minute). PA0 (3) Monitoring--provide a convenient method of determining if the chemcials are being metered properly. PA0 (4) Noncritical Malfunctions--should the system malfunction, it should do so in a manner as not to damage a lawn (i.e., if metering is in error it will not over feed a particular chemical). PA0 (5) Adaptable--the system must be adaptable to current mobile units already in use. PA0 (6) Simple--simple to operate and maintain with crews that are primarily trained to deal with unsophisticated mechanical and electrical systems. PA0 (7) Efficient--negligible increase in time to operate the system as compared with current known systems. PA0 (8) Reliable--the equipment must be able to withstand the vibration and jolts from truck mounting as well as the corrosive effect of the chemicals.
Basic application methods have included the use of dry granular chemicals, liquid suspension, and soluble liquids.
The use of dry chemicals has not gained widespread acceptance since the narrow width of the spreader limits the rate of application and increases the amount of time required for treatment.
A liquid suspension or slurry involves the use of solids that require agitation in order to avoid their settling out of the solution. Such method is not in widespread use because it affords no significant advantage, but increases the complexity and cost of the application equipment.
The spraying of liquid chemicals from a single premixed batch tank is becoming a popular form of application. In this type system all chemicals that are to be sprayed during the day are mixed in a large tank mounted on a truck. A pump, ordinarily driven by the truck engine, provides the required pressure for a spray gun used by the operator. Since the lawn may have confined or narrow areas due to shrubbery and borders, the operator must vary his walking speed and the rate of discharge of the liquid to apply the proper amount to each area.
Disadvantages of the foregoing liquid chemical system include (a) the premixture of chemicals may not exactly suit the requirements of a particular lawn; (b) certain products, particularly insecticides, break down rapidly after being mixed; and (c) disposal of unused mixture in the tank may present a problem.
The present invention, in common with other known systems, meters selected chemical solutions into the spray line, thereby eliminating premixing, and permitting the user to select and apply the desired chemical substances for each lawn without increasing the preparation or the application time. The advantages of this include that material cost may be reduced since unnecessary chemicals are eliminated. Furthermore, since the chemicals are mixed just prior to application, their effective life is extended. A further advantage is that the particular problem of disposing of unused pesticide contaminated sludge is avoided.
Presently available metering systems are generally of two types, proportional metering, or injection. One proportional metering type is powered by line pressure in which a waterwheel measures the flow rate. These are inherently inaccurate when metering low flow rates as occur in lawn spraying and their inability to tolerate relatively high line pressures. A second type of proportional metering device uses a bladder to store the metered chemical and a proportioning valve to control metering. In this type system, as the line pressure increases, the pressure exerted on the bladder also increases permitting the proportioning valve to function independently of line pressure. The principal disadvantages are limited storage capacity, inability to handle wettable powders and lack of flexibility caused by pressure loss in long metered lines.
The injection systems are ordinarily powered by an electrically driven pump, compressed air, or compressed carbon dioxide. Such systems inject at a predetermined flow rate and are, therefore, not capable of proportioning according to the flow rate of fertilizer. In addition the small injection orifices are susceptible to temperature fluctuations, and wear and abrasion resulting in undependable injection rates.
Previously known systems are viewed as unsatisfactory in meeting some or all of the requirements of a lawn spraying system. The requirements are:
The prior art has various flow control proportioning systems for two or more liquids. Thus the patent to Scherer et al. U.S. Pat. No. 3,967,634 discloses a plurality of cylinders that are connected to individual sources of fluid and which can dispense these to a common outlet in a desired proportion, the system control being driven from an additional pressurized source of fluid. Other patents disclosing two or more interconnected cylinders with proportional length leverage connections are disclosed in Robbins U.S. Pat. No. 3,814,289, Buck U.S. Pat. No. 4,002,271, Berrill et al. U.S. Pat. No. 3,386,623, and Pontigny U.S. Pat. No. 3,496,970. Other systems with interconnected proportioning devices are disclosed in Krukemeier U.S. Pat. No. 2,887,094, and Gusmer et al. U.S. Pat. No. 3,765,605.
Pringle et al. U.S. Pat. No. 3,865,308 discloses a plurality of interconnected sources feeding to a single discharge under the control of an operator.